Cationic Polyelectrolytes with Alkylsulfonate Counterions as a Cathode Interface Layer for High-Performance Polymer Solar Cells

Three cationic polyelectrolytes polyethyleneimine ethoxylate (PEIE)–1,4-butanediol dimethylsulfonate (MSB), PEIE–1,4-butanediol diethylsulfonate (ESB), and PEIE–1,4-butanediol dibenzylsulfonate (BSB), containing methylsulfonate, ethylsulfonate, and benzylsulfonate, respectively, were prepared for cathode interface layers (CILs) via a one-step reaction with 1,4-butanediol dialkylsulfonate and PEIE as the reactants. The results indicate that PEIE–MSB and PEIE–ESB with smaller counterions possess more efficient electron extraction, higher electron mobilities, and better photovoltaic performance than PEIE–BSB with larger counterions. The PTB7-Th:PC71BM-based single junction bulk heterojunction polymer solar cells (PSCs) with PEIE–ESB as the CIL showed power conversion efficiencies (PCEs) of 10.44 and 9.23% under the thickness conditions of 8 and 30 nm, respectively. The PM6:Y6-based PSCs displayed a high PCE of 15.69%. The study provides not only new high-performance CILs but also a new strategy to construct light-soaking-free PSCs via tuning alkylsulfonate counterions.